1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and particularly relates to a liquid ejection head in which droplets are ejected from nozzles.
2. Description of the Related Art
There are known image forming apparatuses that employ an inkjet system in which ink droplets are ejected from a plurality of nozzles provided in a print head (liquid ejection head) to form images on a recording medium. Such image forming apparatuses require a high density in the nozzles, high frequency driving, and the ejection of highly viscous ink in order to achieve high quality in the images and to perform high speed printing.
Various configurations for print heads have been proposed (see Japanese Patent Application Publication Nos. 2001-179973, 2001-353871, 9-226114, 2002-36547, 2002-86724, and 2002-264331, for example).
Japanese Patent Application Publication No. 2001-179973 discloses a configuration in which a common ink chamber (ink supply tank) is disposed on the side of the pressure chambers (pressure generating chambers) opposite the side on which the nozzles are formed. In this configuration, an adhesive layer, a flow channel forming substrate, a cavity forming substrate including a cavity as a pressure chamber, and a diaphragm are layered in this order from the ink ejecting side. Piezoelectric elements (piezoelectric vibrating elements) are disposed on the side of the diaphragm opposite the side facing the cavity forming substrate. A common liquid chamber configured from wall designed to enclose the piezoelectric elements is then disposed on the sides of the piezoelectric elements of the diaphragm. In this configuration, ink is supplied to the pressure chambers from the common liquid chamber through tiny supply holes formed in the diaphragm, ink supply holes formed in the cavity forming substrate, and communicating holes formed in the flow channel forming substrate.
However, in the configuration disclosed in Japanese Patent Application Publication No. 2001-179973, there are problems with poor refilling properties, because the ink held in the common liquid chamber is supplied to the pressure chambers from above the pressure chambers (the side of the pressure chambers opposite the side on which the nozzles are formed) by means of the communicating holes positions below the pressure chambers (the side of the pressure chambers on which the nozzles are formed). This configuration also has a flexible cable as an external wire connected to one end of the diaphragm, wherein the drive electrodes of the piezoelectric elements are arrayed along the surface of the diaphragm. Therefore, these wiring spaces might be insufficient when the piezoelectric elements are arranged at a high density.
Japanese Patent Application Publication No. 2001-353871 discloses a configuration in which a common liquid chamber (reservoir) is disposed on the side of the pressure chambers (pressure generating chambers) opposite the side on which the nozzles are formed. In this configuration, piezoelectric elements (piezoelectric vibrating elements) are disposed on a diaphragm (flow channel sealing plate) constituting one wall of the pressure chambers, and the common liquid chamber is disposed at a position corresponding to a portion on the diaphragm other than the areas where the pressure chambers are aligned. The portion of the diaphragm corresponding to the common liquid chamber opening is a thin portion, and is designed to absorb fluctuations in ink pressure.
However, the configuration disclosed in Japanese Patent Application Publication No. 2001-353871 is designed with the common liquid chamber disposed at a position on the diaphragm corresponding to the portion other than the area where the pressure chambers are aligned. Specifically, the configuration is designed so that the common liquid chamber cannot be disposed directly above the pressure chambers and ink cannot be directly supplied to the pressure chambers, which is not suitable for a high density arrangement of the pressure chambers. Moreover, the wiring configuration for electrically connecting the drive electrodes of the piezoelectric elements to the external wiring is not taken into account. Therefore, the wiring spaces for electrically connecting to the external wiring might be insufficient when the piezoelectric elements are arranged at a high density.
Japanese Patent Application Publication No. 9-226114 discloses a configuration in which a common liquid chamber (reservoir) is disposed on the side of the pressure chambers opposite the side on which the nozzles are formed. In this configuration, piezoelectric elements are disposed on a diaphragm constituting one wall of the pressure chambers, the common liquid chamber is formed on the side of the diaphragm with the piezoelectric elements, and the ink chambers are communicated with the common liquid chamber through supply holes formed in the diaphragm.
However, in the configuration disclosed in Japanese Patent Application Publication No. 9-226114, the wiring configuration for electrically connecting the drive electrodes of the piezoelectric elements to the external wiring is not taken into account. Therefore, the wiring spaces for electrically connecting to the external wiring might be insufficient when the piezoelectric elements are arranged at a high density.
Japanese Patent Application Publication No. 2002-36547 discloses a configuration in which a common liquid chamber (common ink chamber) is disposed on the same side of the pressure chambers (pressure generating chambers) on which the nozzles are formed. In this configuration, piezoelectric elements are disposed on a diaphragm (elastic film) constituting the top walls of the pressure chambers, and a protective cover (bonding substrate) formed from glass covers the piezoelectric elements. The common liquid chamber is formed on the ink ejecting side of the nozzle plate on which the nozzles are formed (the side opposite the pressure chambers), and the common liquid chamber is communicated with the pressure chambers through ink supply holes, each of which is formed at a position in the nozzle plate corresponding to an end of each of the pressure chambers.
However, the configuration disclosed in Japanese Patent Application Publication No. 2002-36547 is designed with the drive electrodes of the piezoelectric elements connected to the external wiring through a lead electrode running along the diaphragm. Since the piezoelectric elements are arranged on the diaphragm, these wiring spaces might be insufficient when the piezoelectric elements are arranged at a high density. This configuration also has problems with poor properties in terms of refilling the pressure chambers with ink from the common liquid chamber, because the common liquid chamber is provided to the ink ejecting side of the nozzle plate.
Japanese Patent Application Publication No. 2002-86724 discloses a configuration in which a common liquid chamber (reservoir) is disposed on the side of the pressure chambers (pressure generating chambers) opposite the side on which the nozzles are formed. In this configuration, piezoelectric elements are disposed at positions that face the pressure chambers across a diaphragm (elastic film) constituting the top walls of the pressure chambers, and a protective cover (sealing member) formed from silicon divides and seals the piezoelectric elements with dividing walls. The common liquid chamber is disposed on the piezoelectric element side of the pressure chambers at a different area from where the piezoelectric elements are arrayed.
However, in the configuration disclosed in Japanese Patent Application Publication No. 2002-86724, the wiring configuration for electrically connecting the drive electrodes of the piezoelectric elements to the external wiring is not taken into account. Therefore, the wiring spaces for electrically connecting to the external wiring might be insufficient when the piezoelectric elements are arranged at a high density. Moreover, the configuration is designed with the pressure chambers on the diaphragm aligned in one row, and the common liquid chamber is provided so as to be aligned along this row of pressure chambers, which is not suitable for a high density arrangement of the pressure chambers.
Japanese Patent Application Publication No. 2002-264331 discloses a configuration in which a common liquid chamber (reservoir) is disposed on the pressure chambers (pressure generating chambers) on the same side on which the nozzles are formed. In this configuration, the walls of the pressure chambers on the nozzle side are configured from a diaphragm (elastic film), and the piezoelectric elements are disposed at positions that face the pressure chambers across the diaphragm. The common liquid chamber is formed on the ink ejecting side of a sealing plate on which the nozzles are formed (the side opposite the pressure chambers) at a position corresponding to the end of the sealing plate. The pressure chambers are formed by the half-etching of silicon, and are provided with atmosphere communicating holes (through-holes) embedded in the bottom faces.
However, the configuration disclosed in Japanese Patent Application Publication No. 2002-264331 is designed with the drive electrodes of the piezoelectric elements connected to the external wiring through a lead electrode running along the surface of the diaphragm, and since the piezoelectric elements are arranged on the diaphragm, these wiring spaces might be insufficient when the piezoelectric elements are arranged at a high density.